An air-conditioning system of a vehicle typically comprises a fan for the driving of air. The air which is to be air-conditioned can be drawn in here from an environment of the vehicle, this being so-called “fresh air”. Likewise, the air which is to be air-conditioned can be drawn in from the interior of the vehicle, this being so-called “circulating air”. In order to be able to switch over between a drawing in of fresh air and a drawing in of circulating air, the air-conditioning system can be equipped with a control device, which has a circulating air inlet for the drawing in of circulating air from the interior, a fresh air inlet for the drawing in of fresh air from the environment of the vehicle, and an air outlet for passing the drawn in circulating air or respectively fresh air on to the fan. Furthermore, such a control device can be equipped with a control valve, which is adjustable between a circulating air position, in which it blocks a fresh air path leading from the fresh air inlet to the air outlet, i.e. closes it, and frees a circulating air path leading from the circulating air inlet to the air outlet, i.e. opens it, and a fresh air position, in which it closes the circulating air path and opens the fresh air path.
For reasons of comfort, it is frequently desired that also for the case where the control valve is adjusted into the fresh air position a certain proportion of circulating air is drawn in, so that ultimately also in the fresh air position a mixture of fresh air and circulating air is supplied to the fan.
In order to realize this, it is basically conceivable to configure the control valve so that in the fresh air position it cannot completely close the circulating air path, so that therefore a certain leakage is accepted. A problem here is that, depending on the pressure conditions in the fresh air position, fresh air can emerge through the circulating air inlet into the interior of the vehicle through the leaky control valve, which is undesirable. In order to avoid such a through-flow of the circulating air inlet, it is basically possible to arrange a non-return check valve upstream of the circulating air inlet or between the circulating air inlet and the control valve, which non-return check valve permits a through-flow in a direction leading to the air outlet and blocks a through-flow in an opposite direction leading the circulating air inlet. However, the integration of such a non-return check valve requires a comparatively large amount of installation space.
From DE 10 2010 042 163 A1 a non-return check valve is known, which can basically be used in such a control device, in order to arrange it there for example upstream of the circulating air inlet.
From DE 699 19826T2 an air-conditioning system is known which has a mixing device, which comprises a cold air inlet for cold air, a hot air inlet for hot air and an air outlet for passing on the supplied cold air and/or hot air. In addition, this mixing device is equipped with a mixing valve, into which a bypass contour is worked, wherein this bypass contour is only opened in intermediate positions of the mixing valve, in order to enable an additional cold air flow, whereby the mixing with the hot air flow is to be improved.